Soft gelatin encapsulation of a solution or dispersion of a pharmaceutical agent in a liquid carrier or a water-soluble gel offers many advantages over other dosage forms such as coated or uncoated compressed solid tablets or bulk liquid preparations. Gelatin encapsulation of a solution or dispersion permits the accurate delivery of a unit dose, an advantage which becomes especially important when relatively small amounts of the active ingredient must be delivered, as in the case of certain hormones. Such accuracy is more difficult to achieve via a tabletting process wherein solids must be uniformly mixed and compressed, or by incorporation of the total dose of the active ingredient into a bulk liquid carrier which must be measured out prior to each oral administration.
Soft gelatin encapsulation provides a dosage form which is more readily accepted by patients, since the capsules are easy to swallow and need not be flavored in order to mask the unpleasant taste of the active principle. Soft gelatin capsules are also more easily transported by patients than bulk liquids since only the required number of doses need be removed from the package.
Soft gelatin encapsulation further provides the potential to improve the bioavailability of pharmaceutical agents in the gastrointestinal tract. In the case of an oral liquid preparation, a significant amount of the active ingredient may be lost in the mouth or esophageal lining, prior to absorption into the blood. In contrast, with soft gelatin capsules, the active ingredients are rapidly released as soon as the gelatin shell ruptures. Complete disintegration and dissolution of the capsule are not necessary for the active ingredients to become available for absorption as in the case of tabletted compositions. Also, relatively insoluble active ingredients can be dispersed in a liquid or gelled carrier to provide faster absorption. For example, Miskel et al. (U.S. Pat. No. 3,851,051) discloses soft gelatin capsules which contain aqueous solutions or suspensions of active ingredients in a water-soluble gel lattice matrix which is formulated to rapidly disperse upon rupture of the capsule shell. The rapid action of the active ingredient is ascribed to the high water content of the simple gel (5-20%) and the absence of an oil vehicle. The encapsulation of solutions or dispersions of biologically-active compounds in soft gelatin capsules is disclosed in U.S. Pat. Nos. 4,486,412 and 3,784,684.
Formulations intended for the controlled release of pharmaceutically-active compounds in vivo include solid particles of the active ingredient which are coated or tabletted with film-forming polymers, waxes, fats, silica, and the like. These substances are intended to inhibit the dissolution, dispersion or absorption of the active ingredient in vivo. Although these compositions might be encapsulated in soft gelatin with equipment modifications, the use of such controlled release medicaments can negate many of the advantages associated with the use of liquid filling compositions, such as the ability to uniformly deliver an accurate dose of the active ingredient.
Therefore, a need exists for controlled-release compositions which are suitable for, and compatible with, soft gelatin encapsulation.
A further need exists for gelatin-encapsulated compositions which can release an accurate dose of a medicament therefrom at a controlled rate following rupture of the capsule shell. A need also exists for methods for the preparation of gelatin-encapsulated, controlled-release compositions which can uniformly deliver a unit dose of one or more pharmaceutically active compounds in vitro or in vivo.